2,356 research outputs found
Situación actual de la COX-2 en oncología veterinaria
La enzima prostaglandina G/H sintetasa, también conocida como ciclooxigenasa (COX), controla la síntesis de prostaglandinas a partir del acido araquidónico. Se reconocen fundamentalmente dos isoformas de esta enzima que son denominadas COX-I y COX2. En la actualidad sabemos que un importante número de tumores sobrexpresan (sobreexpresan) la COX-2, mientras que esto no sucede en los tejidos normales de los cuales proceden. Este artículo pretende actualizar la información referente a la COX-2 y su implicación en oncología veterinaria
Demixing and orientational ordering in mixtures of rectangular particles
Using scaled-particle theory for binary mixtures of two-dimensional hard
particles with rotational freedom, we analyse the stability of nematic phases
and the demixing phase behaviour of a variety of mixtures, focussing on cases
where at least one of the components consists of hard rectangles or hard
squares. A pure fluid of hard rectangles may exhibit, aside from the usual
uniaxial nematic phase, an additional (tetratic) oriented phase, possessing two
directors, which is the analogue of the biaxial or cubatic phases in three-
dimensional fluids. There is computer simulation evidence that the tetratic
phase might be stable with respect to phases with spatial order for rectangles
with low aspect ratios. As hard rectangles are mixed with other particles not
possessing stable tetratic order by themselves, the tetratic phase is
destabilised, via a first- or second-order phase transition, to uniaxial
nematic or isotropic phases; for hard rectangles of low aspect ratio tetratic
order persists in a relatively large range of volume fractions. The order of
these transitions depends on the particle geometry, dimensions and
thermodynamic conditions of the mixture. The second component of the mixture
has been chosen to be hard discs or disco-rectangles, the geometry of which is
different from that of rectangles, leading to packing frustration and demixing
behaviour, or simply rectangles of different aspect ratio. These mixtures may
be good candidates for observing thermodynamically stable tetratic phases in
monolayers of hard particles. Finally, demixing between fluid
(isotropic--tetratic or tetratic--tetratic) phases is seen to occur in mixtures
of hard squares of different sizes when the size ratio is sufficiently large.Comment: 27 pages, 9 figure
Mathematical and Anthropological Analysis of Northern Luzon Funeral Textile
The study presents a mathematical analysis and provides an anthropological perspective of the funeral textile of the indigenous communities in northern Luzon, Philippines. In particular, a symmetry analysis is performed, based on principles of group theory and transformation geometry, on the various repeating patterns found in funeral garments and blankets. Results show that particular frieze groups and plane crystallographic groups are favored due to choice of motifs which are reflective of cultural beliefs and funeral traditions, as well as weaving style and methodology. The results of the analysis point to the depth of mathematics present in the work of the weaver, who is able to arrive at meaningful geometric designs without formal training in mathematics. This study contributes directly to the branch of mathematics pertaining to mathematical crystallography in art and cultural heritage which deals, among others, with the use of group theoretic methods and tools in mathematical crystallography to understand the mathematics in artworks arising from various cultures all over the world. It provides further data and analysis to the growing body of literature that uses symmetry to enhance interpretation of culture from the artistic style of its artifacts
A Systematic Search for High Surface Brightness Giant Arcs in a Sloan Digital Sky Survey Cluster Sample
We present the results of a search for gravitationally-lensed giant arcs
conducted on a sample of 825 SDSS galaxy clusters. Both a visual inspection of
the images and an automated search were performed and no arcs were found. This
result is used to set an upper limit on the arc probability per cluster. We
present selection functions for our survey, in the form of arc detection
efficiency curves plotted as functions of arc parameters, both for the visual
inspection and the automated search. The selection function is such that we are
sensitive only to long, high surface brightness arcs with g-band surface
brightness mu_g 10. Our upper limits on
the arc probability are compatible with previous arc searches. Lastly, we
report on a serendipitous discovery of a giant arc in the SDSS data, known
inside the SDSS Collaboration as Hall's arc.Comment: 34 pages,8 Fig. Accepted ApJ:Jan-200
Indirect Off-Axis Holography for Antenna Metrology
Phase acquisition in antenna measurement, especially at millimeter- and submillimeter-wave frequencies, is an expensive and challenging task. The need of a steady phase reference demands not only a very stable source but unvarying temperature conditions and strong positioning accuracy requirements. Indirect off-axis holography is an interferometric technique that allows for characterization of an unknown field by means of a simple filtering process of the hologram or intensity interference pattern in the spectral domain, provided that the reference field, employed to interfere with the unknown field, is known in amplitude and phase. This technique can be used to avoid the effect of the errors related to the phase acquisition and to further develop new efficient and robust techniques capable of phase retrieval from amplitude-only acquisitions allowing for cost and complexity reduction of the measurement setup. A short review of the state-of-the-art in antenna metrology is presented in this chapter, as well as a description of conventional indirect off-axis techniques applied to this field. Last sections are devoted to the description of novel measurement techniques developed by the authors in order to overcome the main limitations of the conventional methods
Isolated spin qubits in SiC with a high-fidelity infrared spin-to-photon interface
The divacancies in SiC are a family of paramagnetic defects that show promise
for quantum communication technologies due to their long-lived electron spin
coherence and their optical addressability at near-telecom wavelengths.
Nonetheless, a mechanism for high-fidelity spin-to-photon conversion, which is
a crucial prerequisite for such technologies, has not yet been demonstrated.
Here we demonstrate a high-fidelity spin-to-photon interface in isolated
divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that
divacancies in 4H-SiC have minimal undesirable spin-mixing, and that the
optical linewidths in our current sample are already similar to those of recent
remote entanglement demonstrations in other systems. Moreover, we find that
3C-SiC divacancies have millisecond Hahn-echo spin coherence time, which is
among the longest measured in a naturally isotopic solid. The presence of
defects with these properties in a commercial semiconductor that can be
heteroepitaxially grown as a thin film on shows promise for future quantum
networks based on SiC defects.Comment: 26 pages, 4 figure
Completeness of classical spin models and universal quantum computation
We study mappings between distinct classical spin systems that leave the
partition function invariant. As recently shown in [Phys. Rev. Lett. 100,
110501 (2008)], the partition function of the 2D square lattice Ising model in
the presence of an inhomogeneous magnetic field, can specialize to the
partition function of any Ising system on an arbitrary graph. In this sense the
2D Ising model is said to be "complete". However, in order to obtain the above
result, the coupling strengths on the 2D lattice must assume complex values,
and thus do not allow for a physical interpretation. Here we show how a
complete model with real -and, hence, "physical"- couplings can be obtained if
the 3D Ising model is considered. We furthermore show how to map general
q-state systems with possibly many-body interactions to the 2D Ising model with
complex parameters, and give completeness results for these models with real
parameters. We also demonstrate that the computational overhead in these
constructions is in all relevant cases polynomial. These results are proved by
invoking a recently found cross-connection between statistical mechanics and
quantum information theory, where partition functions are expressed as quantum
mechanical amplitudes. Within this framework, there exists a natural
correspondence between many-body quantum states that allow universal quantum
computation via local measurements only, and complete classical spin systems.Comment: 43 pages, 28 figure
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